Large scale cellular networks can include a distribution of base stations, each connected to an antenna mounted on a cell tower, for serving a respective cell area. The target density of the distribution of cell towers is such that gaps between cell areas are few in number, and are typically located in unpopulated regions. The necessary cell tower density, in terms of towers per unit area, is therefore determined in part by the size of the cell area, i.e., the area that each tower can serve. Factors determinative of the size of the cell area include the power levels radiated by the cell tower and by the user devices, and by the propagation characteristics of the radio signals by which the cell tower and the user devices communicate. Propagation characteristics include the ability to penetrate building walls, and are determined in part by the frequency of the radio signal. For example, current third generation (3G), fourth generation (4G) and Long-Term Evolution (LTE) systems use signals in frequency ranges that sufficiently penetrate many types of building walls to enable communication with interior user devices, and are generally not impeded by foliage.
The frequency spectrum used by cellular networks is expanding, for reasons such as fifth generation (5G), to include frequencies of 14 GHz and higher. The wavelengths at such frequencies are in the millimeters. Millimeter wave signals, however, do not generally propagate as well in cell environments as do lower frequencies. For example, mm waves can be obstructed by building walls and substantially attenuated by foliage. The result can be significantly smaller cell area than available with frequencies typically used by 3G, 4G and LTE systems. A potential solution is to install a higher density of cell towers.